1. Field of the Disclosure
The present application relates to an organic light emitting display device. More particularly, the present application relates to an organic light emitting display device adapted to form a capping layer in a uniform thickness regardless of kinds of sub-pixels and secure a high luminous efficiency characteristic.
2. Description of the Related Art
Nowadays, a display field for visually representing an electrical information signal has been rapidly developed with the spread of information society. In accordance therewith, a variety of flat panel display devices with features, such as slimness, light weight and low power consumption have been developed. Also, the flat panel display devices have been rapidly replacing the existing cathode ray tubes (CRTs).
As examples of the flat panel display devices, liquid crystal display (LCD) devices, organic light emitting display (OLED) devices, electrophoretic display (electric paper display (EPD)) devices, plasma display panel device (PDPs), field emission display (FED) devices, electroluminescence display devices (ELDs), elector-wetting display (EWD) devices, and so on can be introduced. Such flat panel display devices commonly include a flat display panel, which realizes an image, as a necessary component. The flat display panel is configured with a pair of combined substrates which face each other with having an inherent light emitting or polarizing material layer therebetween.
Among the flat panel display devices, the OLED device includes an organic light emitting element corresponding to a self-luminous element. As such, the OLED device is not necessary for any light source which is used in the LCD device corresponding to a non-luminous device. In accordance therewith, the OLED device can become lighter and thinner. Also, the OLED device has features wider viewing angle, superior contrast ratio, lower power consumption, lower driving DC (direct current) voltage and higher response time compared to the LCD device. Moreover, the OLED device includes soled components. Therefore, the OLED device can well endure external impacts and is driven in a wide temperature range.
The organic light emitting element used in the OLED device includes an anode electrode, a cathode electrode and an organic emission layer which are formed on a substrate. The organic emission layer is interposed between the anode and cathode electrodes. The anode electrode is formed from a transparent conductive material such as indium tin oxide ITO, the cathode electrode is formed from a metal such as aluminum Al, and the organic emission layer is formed from an organic material. Such an OLED device applies an electric field to the organic emission layer in order to emit light.
When a voltage is applied between the anode and cathode electrodes of the organic light emitting element, holes injected from the anode electrode and electrons injected from the cathode electrode are drifted toward the organic emission layer. Also, the holes and the electrons are recombined with each other within the organic emission layer, thereby generating excitons. As such, the OLED device can use light which is emitted by a transition of the excitons from an excited (or triplet) state into a ground state.
An OLED device of the related art can be manufactured in a top-emission mode suitable to emit light in a frontward direction. The top-emission mode OLED device can include: a lower electrode with a reflective film; an organic emission layer; and an upper electrode corresponding to a semi-transparent electrode. In order to raise light efficiency, the top-emission mode OLED device can further include a capping layer which is formed on the upper electrode and used as an optical adjustment (or control) layer. The capping layer adjusts a difference of the refractive index with the exterior (or the atmosphere) and raises the reflectance of its interfacial surface with the exterior (or the atmosphere). This reflectance increment can induce the capping layer to generate a micro-cavity effect for a fixed wavelength band. The capping layer can be formed from an organic material. Alternatively, in order to maximize the micro-cavity effect, the capping layer can be from an inorganic material with high reflectance. The inorganic capping layer can provide features of higher luminous efficiency and lengthier life time compared to the organic capping layer.
FIG. 1 is a data sheet illustrating the luminous efficiency characteristic of the related art OLED device with respect to the thickness of a capping layer.
Referring to FIG. 1, luminous efficiencies of color sub-pixels to the thickness of an inorganic material which is used to form a capping layer of the related art OLED device are illustrated. Light emitted from the organic light emitting element can have one of different wavelengths which are determined according to whether the organic light emitting element is used in anyone of red, green and blue sub-pixels. In accordance therewith, as seen from FIG. 1, it is evident that the optimum thickness of the capping layer which can maximize the luminous efficiency must be different according to the red, green and blue sub-pixels.
However, the related art OLED device forces the capping layer to be formed in the same thickness for every sub-pixel without considering optimum thicknesses in accordance with kinds of sub-pixels. Due to this, it is difficult to secure the maximum luminous efficiency for each of the color sub-pixels. Alternatively, the related art OLED device can allows the thickness of the capping layer to be different according to kinds of sub-pixels. In this case, different chambers must be used in the manufacture procedure of the OLED device. Due to this, productivity for the OLED device must deteriorate.
In other words, it is possible for the related art OLED device to realize only one of the maximum luminous efficiency and high productivity.